Milford -- The "barrier building" at General Motors Co.'s Milford Proving Grounds didn't always have a roof. In fact, it wasn't always a building.

For a long time, it was just a barrier -- a 140,000-pound rock strapped to the bedrock under Milford.

It is an unmovable object, a stone that has endured 17,269 collisions (and still counting). And it has never budged an inch. It's the centerpiece of what GM calls the barrier building and a building block for the automaker's Vehicle Safety and Crash Worthiness Lab.

GM has been smashing up vehicles since the 1930s and started using the barrier block in 1962.

In 2006, GM upgraded its facility to the tune of $33 million and added a $10 million rollover crash facility. All told, safety engineers conduct more than 50 different tests and evaluate reams of data produced at the facility.

Now, GM is finishing its testing on the Chevrolet Cruze, a compact car set to arrive in September.

As smaller cars take on a bigger role in the U.S. auto market, places like GM's safety center will play an even more important role, as engineers look for ways to make a little car hold up to a bigger one in a collision. GM expects a five star crash rating when the Cruze undergoes independent testing. It knows this based upon its performance in Milford..

Albert Ware, the lab director, said the initial safety testing is done through computer modeling and then results are verified through physical crash testing.

"The depth of testing is incredible," he said.

Evolving methods

Drivers used to stand on car running boards and then hurl vehicles at the rock, jumping off at the last second, moments before the vehicle collided into the stone in a crude form of safety chicken.

Observers would evaluate how well the car performed and study the effects of the impact.

Now, it takes five days to prepare a vehicle for a crash test. Thousands of pictures will be taken, crash test dummies will sit inside the vehicle and scientists will spend weeks sifting through the data collected during the 1/10th of a second it takes to demolish a vehicle.

Scientists will evaluate airbags, steel performance, energy flow and a host of other things happening during that tiny fraction of time.

The facility has a small tribe of crash test dummies -- approximately 400 -- which can cost as much as $150,000 per dummy to sit inside vehicles. They are filled with instruments that can measure the effects of a crash throughout their bodies. These dummies come in all shapes and sizes, from infants to overweight men; though the 50th percentile American is a 5-foot-8 man weighing about 180 pounds.

GM also has a giant hydraulic sled that can simulate a car crashing without actually damaging the vehicle. Basically, workers strap a car to the sled, then it simulates a crash. It's used to test things like airbag deployments and how bodies in the vehicles react to an accident, said Terrilynn Tavcy, who oversees testing on the sled.

The sled has saved thousands of vehicles from crash tests.

Other GM scientists and engineers use dummy pieces to test things like the impact of a head on roof liner. Basically, the heads are shot into roof liners to measure impact and potential damage.

'We only get one chance'

For the Cruze, engineers will eventually demolish 20 to 30 vehicles to verify and test its safety construction to U.S. standards, said Paul Simpson, the engineering group manager at the facility.

Typically, up to 70 vehicles are smashed up, but the Cruze, currently sold in 60 countries outside of North America, has already passed other countries' safety regulations. Some vehicles endure more than one crash test, though eventually all of them are crushed and recycled.

"The entire crash takes a blink of an eye," Simpson said, "and we only get one chance to capture all of the information."

The rollover facility is the newest addition to the crash worthiness lab has taken on additional importance since the National Traffic Highway Safety Administration increased roof crush standards on vehicles.

The idea is to test the vehicles stability control and then ultimately have the side curtain airbags fire, Ware said. However, the car also needs to know when not to deploy the airbags, such as when a car drives into a ditch and doesn't flip.

Perhaps the most interesting part of the tour was toward the end when the group was presented with a number of Cruze bodies post crash testing.

Even after a 31 mph impact from a battering ram -- made to simulate a Ford F-150's front end hitting the Cruze in the side -- the cabin was completely intact and the doors still opened.

Certainly, the occupants would be bruised and slightly battered, but their chances of living to talk about it are significantly better than ever before.